Gary W. Moorman, Professor of Plant Pathology
|Cedar-apple rust||Smooth, round galls on twigs are up to golf ball size. Their surface may be dimpled like a golf ball.||Gymnosporangium juniperi-virginianae||Prune and destroy galls before the spore horns develop. In the nursery, apply a fungicide in the mid July through August.|
|Cedar-quince, cedar-hawthorn, and Japanese apple rust||Young leaves and twigs have bright-orange spots that look like paint splatters in the spring. These spots darken and become dull orange to rust colored. Slight twig swellings are not obvious except in the spring when their surface is orange with spores. The bark on infected twigs flakes away, growth slows, and twigs die back.||Gymnosporangium clavipes (cedar-quincerust)
Gymnosporangium globosum (cedar-hawthorn rust)
Gymnosporangium yamadae (Japanese apple rust)
|Prune and destroy galls before the spore horns develop. In the nursery, apply a fungicide in the mid July through August.|
|Cercospora blight||In the summer, needles become bronzed, tan, and eventually gray. The needles of the inner and lower branches are affected first. The disease progresses upward on the shrub and outward toward the branch tips. This differs from twig blights which start at branch tips. Dark fungal fruiting structures break through the surface of infected needles. Microscopic examination of the spores reveals dark, multicelled spores that are longer than they are wide. Affected branches thin and fall, giving the shrub an open, bare appearance.||Cercospora sequoiae var. juniperi||The fungus over-winters on the plant, spores are present all year, and infection can occur when temperatures are mild and moisture is on the needles. Removal of the plant is better than attempting to control this disease with fungicides. However, a fungicide can be used.|
|Twig blight||Tips of branches die and turn brown or ash gray. These remain on the shrub for many months. Larger branches can be invaded and girdled. On the dead tissue where it meets the still-living wood, small, black, pimple-like fungal fruiting structures form. Microscopic examination reveals oval, colorless spores. See Phomopsis below.||Kabatina or Phomopsis
||Prune and destroy infected twigs and branches. It is possible for both Kabatina and Phomopsis to cause twig blight on the same plant. Apply a fungicide whenever new growth is present on the shrub.|
Cedar-apple rust galls at dormancy in winter, early telial horn emergence, and full telial horn emergence in the Spring.
Cedar-quince or cedar-hawthorn rust gall at a very young stage and an older gall with telial horn emergence.
Twig blight by either Phomopsis or Kabatina . Microscopic examination of the fruiting structures and spores is required to determine which fungus is involved. Phomoposis produces two spore types in a pycnidium while Kabatina forms one type of spore in an ascervulus.
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